In a conventional ink-jet printer, sheet media are directed through a print cycle which includes picking up a sheet from an input tray, feeding it through the printer's printing zone, and then expelling it through an output port. Once expelled, the sheet falls to an output tray, consecutive sheets piling one on top of the other to form an output stack. Because ink-jet printers print using wet ink, and because sheets often are stacked immediately after printing, ink-jet printers have in the past experienced difficulty with blotting and/or smearing of ink upon contact between consecutively printed sheets. This has been particularly apparent where the ink drying time exceeds the time between printing of consecutive sheets. Although a variety of solutions have been proposed to deal with this problem, none have provided adequate ink drying time without some cost to the printer's efficiency, versatility or size.
Some manufacturers have, for example, attempted to eliminate ink smearing and blotting problems by decreasing the ink's drying time. One solution has been to employ quick-drying ink, or specially coated paper. These products, however, have not always been available, and have often produced poor quality print. Another solution has been to provide some sort of drying lamp or heater adjacent the printed media, but this adds to the complexity of the printer, and consequently adds to the printer's price.
Other manufacturers have attempted to delay the deposit of printed sheets in the output tray so as to provide the previously-printed sheet with adequate drying time. The most basic of such solutions have involved simply slowing printer throughput by creating an artificial time delay between the printing of consecutive sheets. Although this solution does increase the time available for ink to dry, it has proven unacceptable in view of the ever-increasing desire to improve printer efficiency and speed.
Another solution proposed by printer manufacturers has been to employ a passive drop scheme wherein a sheet emerging from the printer's output port is guided along rails which suspend the sheet above the output tray. At the completion of printing, the sheet simply drops of its own weight into the output tray, the previously-printed sheet having had an opportunity to dry during printing of the present sheet. However, passive drop schemes are not always reliable due to a phenomenon known as cockling. As a result of such cockling, sheets do not always drop into the output tray after printing, but instead are pushed forward and out of the printer by the following sheet. This cockling effect becomes more pronounced with environmental extremes and large amounts of ink on the sheet.
Yet another common solution has involved the use of an active drop mechanism wherein a printed sheet is guided along a pair of movable wings which temporarily support the sheet above the printer's output tray. Once printing is completed, the wings retract, often pivotally, allowing the sheet to fall to an output tray below. The previously-printed sheet thus is provided with time to dry during printing of the present sheet. Although generally effective, active wing arrangements generally are not suitable for a wide range of media widths, and can significantly increase the printer's chassis size. Active drop mechanisms also may present problems related to sheet sail, a phenomenon which can result in sheets gliding out of the printer upon retraction of the wings.